One type of bar code reader includes a wand or other read head that can be drawn across a bar code, and which includes a lens for forming an image of a portion of the bar code onto a photocell. The photocell generates an electrical output of a magnitude dependent upon the amount of light thereon; the output is delivered to a detection circuit which detects the passage of light and dark bar elements across the photocell. Such bar code readers are useful both in identifying goods by their bar code, and in verifiers which can verify that a printed bar code label meets certain criteria that enables it to be reliably read by available bar code readers.
Different bar code formats are used in different geographic locations, wherein the densities of the bar code elements vary. That it, the minimum widths of the light and dark bar code elements are different for different types of bar codes. There are businesses that must read bar codes of different densities, such as warehouses that receive goods from different parts of the world bearing bar codes of different densities. Also, verifiers sometimes have to be used on bar codes of different densities. It may be noted that while previous verifiers tended to detect multiple characteristics along the width of each bar element, more recent standards have specified verifiers which act like readers used in stores and warehouses which have similar photocells in the readers.
The photocells which detect images of bar code elements passing thereacross, preferably have a diameter about 80% of the width of the bar elements of smallest width for the particular bar code to be read. Thus, in a bar code wherein the thinnest elements have a width of 10 mil (one mil equals one thousandth inch) and the optical magnification is one, the photocell preferably has a diameter of 8 mil. Where the optic magnification is four, the photocell preferably has a diameter of 32 mil. Low densities (wide bar elements) are useful as where bar codes are printed on cardboard containers, where the printing is often poor. High densities are useful for printing labels used on small items. Presently, different bar code densities are accommodated by replacing the reader head with a more appropriate one. A bar code reader, used either for product identification or verification of printed labels, which could accurately read bar codes of a range of densities with minimal additional, expense, would be of considerable value.